Well surveying method and apparatus



Feb. 17, 1942. J, NEUFELD WELL SURVEYING METHOD AND APPARATUS FiledApril 22, 1940 Patented Feb. 17, 1942 WELL SURVEYING METHOD ANDAPPARATUS Jacob Neufeld, Tulsa, Okla., assignor to Well Surveys,Incorporated, Tulsa, Okla., a corporation of Delaware Application April22, 1940, Serial No. 331,039

7 Claims.

This invention relates to geophysical prospecting and more particularlyto a method of determining the point of entry intoa well bore and thenature of connate fluids from formations which lie adjacent a well bore.

It has already been suggested that data of this type be obtained bytaking a-series of resistivity versus depth parameters of the fluid inthe well bore, and reducing the hydrostatic pressure between the takingof parameters to cause more of the fluid under investigation to enterbetween the taking of parameters. United States Patents 2,184,338,granted December 26, 1939, to George H. Ennis, and 1,555,800 and1,555,801, granted September 29, 1925, to Frederick'QW. Huber, andBritish Patent 452,076, accepted August 17, 1936, describe processes ofthis kind.

These methods are satisfactory in many instances, but often it isdesirable to distinguish between the entering fluid and the fluidalready in the well or entering from some other point, on differentbasis than resistivity, because there is not suiiicient difference inresistivity to permit the necessary distinctions to be made. Also,occasionally, upon a reduction of the hydrostatic pressure fluid willcome out of a formation behinda casing wall, pass up or down the walland eventually find an opening into the casing. It is desirable, ifpossible, not only to find the opening but also the formation that isthe source of the fluid.

The present invention has for its primary object the accomplishment ofboth of these things. By its use distinction can often be made betweenfluids of the same resistivity and the formation from which the fluidoriginated can often be located even though the fluid passes up or downbehind the casing before entering it.

Briefly, this invention comprises taking a series of radioactivityversus depth parameters, and reducing the hydrostatic pressure betweenthe. taking of parameters. Such a process distinguishes between fluidson the basis of their radioactivity and will detect the fluids eventhough they are separated from the measurin instrument by a steelcasing'wall.

For the purpose of taking the radioactivity parameters any known type ofdevice that will measure radioactivity in a well bore and correlate themeasurements with indications of depth, may be used. It is preferred touse a John C. Bender; in United States Patent 2,133,- 776, grantedOctober 18, 1939, or those shown in application Serial Number 239,781,filed by Robert E. Fearon, on November 10, 1938; application SerialNumber 323,239, filed by this inventor on March 9, 1940; applicationSerial Number 325,880, filed by Robert E. Fearon on March 25, 1940;323,981, filed by Robert E. Fearon on March 14, 1940; application SerialNumber 324,687, filed March 18, 1940, by Jacob Neufeld; applicationSerial Number 326,510, filed March 28, 1940, by Robert E. Fearon, may beused.

The device described in application Serial Number 277,964 comprises ahigh pressure ionization chamber, a source of potential and anamplifier, enclosed in a fluid-tight casing and adapted to be loweredinto a well. Gamma-radiations or the like change the ionization of thechamber, resulting in a change of current. fiow therethrough and theamplifier is controlled by If a series of these parameters are made andfluid removed from the well between'their mak ing, the parameters willshow progressively accentuated peaks at the points where the fluidenters, due to the entry of more and more fluid. If the fluid is moreradioactive than the fluid in the well, the peaks will be in a positivedirection, if less, they will lie in the other direction.-

A peak that starts at one point and then flattens out and reappears at aspaced point will indicate fiuid entry behind a casing at the first'point and entry into the casing at the second point.

The attached drawing and the following detailed description thereof willgive a more complete and detailed understanding of the principles andadvantages of the invention. The sole figure of the drawing -is adiagrammatic illustration of a device for making surveys according tothe principles of this invention.

The device illustrated in the drawing is a relatively simple form of asurveying instrument for the present purpose but -it is to be understooddevice of the type described in this inventors application SerialNumber277,964, filed June '7,

that this device can be modified in accordance with the teachings of anyof the patents or applications mentioned above and information of thetype obtainable according to those patents application Serial Numberandapplications can be used for the same gen eral purpose and theinformation that can be obtained by the relatively simple type of devicehere illustrated.

As shown in the drawing the device may consist of a cylindrical casingl0 adapted to be hermetically sealed and to enclose the necessarymeasuring equipment. This casing is suspended in the well bore by meansof a cable I l which also serves to convey the measuring currents to thesurface of the earth.

Within the casing I0 is an ionization chamber I2 in which is positioneda rodshapecl electrode l3 surrounded by a second electrode [4 preferablyof sheet metal and in the shape of an open ended cylinder. The chamberis filled with an inert gas, preferably argon, under around 1500 to 2000pounds per square inch pressure and connections from the electrodesextend through the walls of the chamber to the outside and, of course,are insulated from the chamber wall.

Outside of the chamber, but within the casing ID, a relatively highresistance 15 and a battery or other source of electrical potential 16are connected in series across the electrodes. Preferably the negativepole of the battery is connected to the cylindrical electrode l4 and thepositive pole is connected through the resistance Hi to the centerelectrode l3. It has also been found desirable to ground the positivepole of the battery to the main casing ID. The battery will preferablyhave a potential of around 150 volts and the resistor a resistance ofaround 10 ohms. Across the resistor I5 an amplifier I1 is connectedwhich serves to amplify the potential drop across the resistor and senda current indicative thereof to the surface through the cable ll.

In operation the intensity of the radiations reaching the inside of theionization chamber l2 governs the internal resistance of the. ionizationchamber and hence the current flow through the resistor l5. This in turngoverns the potential drop across the resistor and hence the signal sentto the surface by the amplifier.

At the, surface the cable ll passes over a measuring wheel l8 and iswound into a cable reel IS. The currents from the cable pass onto sliprings 20 on the cable reel from which they are taken by brushes 2| andpassed to an amplifier 22. From the amplifier -22 they E0 to a recorder23, the tape of which is driven in accordance with the movements of thecasing l0 up and down in the well so as to record the measurements incorrelation with determinations of the depth at which they are taken.

To accomplish the driving of the recorder tape in accordance with themovements of the casing In in the well the recorder is connected to themeasuring wheel l8 through a mechanical or electrical transmissionsystem 24. In actual practice it has been found desirable to use anelectrical transmission system of the type known as the Selsyntransmission system.

4 In practicing the present invention the cable this process thehydrostatic pressure in the well is changed by any desired method, suchfor example, as removing a part of the fluid from the well, andthereafter a new parameter'is taken.

This process can be repeated as many times as is necessary and uponcomparison of the parameters, if a fluid differing in radioactivity fromthat originally in the well enters from some strata along the well borethis will be apparent by progressively increasing peaks in the severalparameters. As already indicated the peak may be in either a positive ora negative direction depending upon whether the fluid which enters thewell is more or less radioactive than the fluid already in the well.

While it is intended that this invention be applied particularly towells filled with liquid and to the determination of entering liquids itis also possible to apply this invention to wells filled with gases andto the entering of gases and under some circumstances it is evenpossible to apply the principles of this invention to a well filled withliquid but into which gas will enter when hydrostatic pressure isreduced or to a well filled with gas and into which liquid will enterwhen pressure is reduced.

Since numerous modifications within the scope of the general principlesof this invention will immediately be apparent to those skilled in theart it is to be understood that this invention is not limited to thespecific embodiment shown or described but only as indicated by thescope of the appended claims.

Iclaim:

1. A method of determining the point of entrance of fluid into a wellbore that comprises taking a radioactivity versus depth parameter of thefluid in the well, reducing the hydrostatic pressure of the fluid in thewell and taking a second parameter of radioactivity versus depth oi thefluid in the well.

2. A method of determining the point of entrance of a fluid into a wellbore that comprises measuring at various depths in the well bore theradioactivity of the fluid in the well bore, simultaneously determiningthe position of each measurement and recording the determination ofposition and the measurement in correlation, reducing the hydrostaticpressure on the fluid in the well bore, repeating the measurements andrecording and comparing the recordings mad prior to and after thereduction of the hydro" static pressure.

3. A method of determining the pointof entrance of fiuid into a wellbore that comprises alternately taking radioactivity versus depthparameters of the fluid in the well bore and reducing the hydrostaticpressure of the fluid in the well bore, and comparing the parameters som the liquid in the well, reducing the hydrostatic ducing thehydrostatic pressure on the liquid in the well bore, repeating themeasurements and recording and comparing the recordings made prior toand after the reduction of the hydrostatic pressure.

6. A method of determining the point of entrance of liquid into a wellbore that comprises alternately taking radioactivity versus depthparameters of the liquid in the well bore and reducing the hydrostaticpressure of the liquid in the well bore, and comparing the parameters soobtained.

7. The methodiof determining the point of en-

